This invention concerns automatically controlled punch presses for forming holes in sheet material workpieces.
In recent years, punch presses have become highly automated, with CNC control over tool selection and positioning of the workpiece in the press to execute a programmed series of punching and forming operations on a sheet material workpiece.
Another trend is to provide a hydraulically operated press ram in order to enable sophisticated control over the punching process, as for example to precisely variably control the punch velocity so as to minimize cycle time and punching noise.
Such hydraulically operated ram presses are equipped with a hydraulic pump designed to supply a flow of sufficiently high pressure fluid to enable execution of the heaviest tonnage punching requirements of which the machine is capable. During execution of the punching program, the pump is normally run at maximum output, regardless of the tonnage requirements of the particular program.
The tonnage required is dependent on the tool size and shape characteristics, as well as the thickness of the workpiece material and its shear strength.
Running the pump at its highest output level is costly in terms of power consumption and increased maintenance of the pump seals, etc, and increased generation of heat and noise is a disadvantage.
Most punching programs do not require the maximum press tonnage to execute. While manual reduction of the pump output for a given program is a possibility, this would increase the difficulty and time required in operating the press and also cause an increase in the possibility of errors in setting up for a programmed production run.
The object of the present invention is to provide a pump output control for hydraulic ram press to reduce the pump output when possible and without requiring the necessity for operator intervention.